1. Field of the Invention
This invention relates to an apparatus for measuring the degree of sugariness of fruit or vegetables such as apples and peaches.
2. Related Background Art
As shown in FIG. 6 of the accompanying drawings, the juice of fruit or a vegetable has heretofore been used as an object 50 to be examined, and the object to be examined has been sandwiched between prisms 52 and 54 having the same refractive index.
In this apparatus, monochromatic visible light from a light source 56 enters the object 50 to be examined through the prisms 52 and 54, and the incident light is refracted by the difference between the refractive indices of the object 50 to be examined and the prisms 52, 54. A line sensor 58 for receiving the refracted light is divided into light and dark portions by the presence or absence of the application of emergent light.
The direction of emergence of the emergent light differs depending on the refractive index of the object to be examined and therefore, the refractive index of the object to be examined can be found from the boundary position of the refracted light which has arrived at the line sensor 58, and further, the degree of sugariness of the fruit or a vegetable which is the object to be examined is obtained (by the relational expression of ICUMSA (International Commission on Uniformity Method of Sugar Analysis) (Table 1).
TABLE 1 Relation between Brix and Refractive Index 1974 ICUMSA % n.sub.D.sup.20 % n.sub.D.sup.20 % n.sub.D.sup.20 % n.sub.D.sup.20 % n.sub.D.sup.20 0 1.33299 20 1.36384 40 1.39986 60 1.44193 80 1.49071 1 1.33442 21 1.36551 41 1.40181 61 1.44420 81 1.49333 2 1.33586 22 1.36720 42 1.40378 62 1.44650 82 1.49597 3 1.33732 23 1.36889 43 1.40576 63 1.44881 83 1.49862 4 1.33879 24 1.37060 44 1.40776 64 1.45113 84 1.50129 5 1.34026 25 1.37233 45 1.40978 65 1.45348 85 1.50398 6 1.34175 26 1.37406 46 1.41181 66 1.45584 86 1.5067 7 1.34325 27 1.37582 47 1.41385 67 1.45822 87 1.5094 8 1.34477 28 1.37758 48 1.41592 68 1.46061 88 1.5121 9 1.34629 29 1.37936 49 1.41799 69 1.46303 89 1.5149 10 1.34782 30 1.38115 50 1.42009 70 1.46546 90 1.5177 11 1.34937 31 1.38296 51 1.42220 71 1.46790 12 1.35093 32 1.38478 52 1.42432 72 1.47037 13 1.35250 33 1.38661 53 1.42647 73 1.47285 14 1.35408 34 1.38846 54 1.42863 74 1.47535 15 1.35568 35 1.39032 55 1.43080 75 1.47787 16 1.35729 36 1.39220 56 1.43299 76 1.48040 17 1.35891 37 1.39409 57 1.43520 77 1.48295 18 1.36054 38 1.39600 58 1.43743 78 1.48552 19 1.36218 39 1.39792 59 1.43967 79 1.48811
In this example, monochromatic visible light is applied to an object 50 to be examined which is the juice of fruit or a vegetable through a prism 62. When the angle of incidence at this time is suitably selected, the incident light is totally reflected by the surface 64 of the object to be examined 50 which is in contact with the prism 62. A line sensor 58 which receives the totally reflected light is divided into light and dark portions by the presence or absence of the application of the reflected light. The angle at which the total reflection begins differs depending on the refractive index of the object to be examined and, therefore, it is similar to the above-described example of the prior art that the refractive index and the degree of sugariness of the fruit or vegetable which is the object to be examined are obtained from the boundary position of the line sensor 58.
In these apparatuses, however, juice had to be picked with the fruit or vegetable destroyed. Therefore, the fruit or vegetable had to be destroyed and consumed each time measurement was done, and the degree of sugariness of the fruit or vegetable to be sold could not be measured.
In contrast with these, an example of the prior art as shown in FIG. 8 of the accompanying drawings is known as a method of measuring an object to be examined without destroying it.
In this example, fruit or a vegetable which is not yet destroyed is used as an object 66 to be examined, instead of the object 50 to be examined in FIG. 7. The principle of measurement is similar to that in the example of FIG. 7.
However, if the contact between the prism 62 and the surface 68 of the object to be examined is insufficient or if air is present near it, total reflection does not take place on the surface 68 of the object to be examined. Also, if the surface of the object to be examined has an inclination angle with respect to the prism 62, accurate measurement cannot be done due to the influence of this inclination angle.
Further, an apparatus using near infrared absorption analysis has been put into practical use as a method of measuring fruit or a vegetable without destroying it, but this apparatus is bulky and expensive, and requires a power source.